This invention relates to an automatic sampling arrangement for supplying liquid samples to an analytical instrument comprising a sample carrier in the form of a turntable with the turntable having a plurality of locations for sample containers arranged in two circles of different radii centered on the axis of rotation of the turntable, and a sampling mechanism for aspirating a sample from a sample container by a sample tube when the turntable is indexed to bring one of the samples in registration therewith.
An atomic absorption spectrophotometer having automatic microprocessor controlled means for carrying out a succession of analyses is described in U.K. Patent Applications Nos. 8133968 (PHB 32832), corresponding to U.S. Ser. No. 617,069, filed June 4, 1984, which is a CIP of Ser. No. 436,207, filed Oct. 25, 1982 and now U.S. Pat. No. 4,431,637; 8201371 (PHB 32848), corresponding to U.S. Ser. No. 450,489, filed Dec. 16, 1982 and now U.S. Pat. No. 4,508,451; 8201372 (PHB 32849), corresponding to U.S. Ser. No. 458,123, filed Jan. 14, 1983 and to be U.S. Pat. No. 4,519,706 and 8201373 (PHB 32850), corresponding to U.S. Ser. No. 456,238, filed Jan. 7, 1983; and is manufactured and sold by Pye Unicam Limited under the type number PU9000. It is desirable for the samples to be made available to such an instrument under the control of the microprocessor.
An automatic sampling arrangement is known from published European Patent Application No. 0,015,025 (PP 1234), corresponding to U.S. Pat. No. 4,302,421, for supplying liquid samples to an analytical instrument, in this case a flameless atomic absorption spectrophotometer. This sampling arrangement comprises a sample carrier in the form of a turntable, the turntable having a plurality of locations for sample containers arranged on a circle centered on the axis of rotation of the turntable and a sampling mechanism for aspirating a sample from a sample container when the turntable is indexed to bring one of the sample locations in registration therewith. In this known sampling arrangement the turntable has only one circular rank of sample locations and also the details of the analytical function to be performed on each sample are encoded on the turntable by mechanical means comprising corresponding circular ranks of holes which are either left open or blocked to form a code corresponding to the function. The turntable is mounted on a central spindle.
Another automatic sampling arrangement is known from British Patent Specification No. 1,596,868 in which the turntable locations for sample containers are arranged on two circles of different radii centered on the turntable axis. The sampling mechanism moves automatically from sample locations on one circle to sample locations on the other circle so that all the containers on the turntable are sampled in a predetermined order. The turntable locations are first loaded with sample containers and then the turntable is lowered onto a central drive spindle connected to an indexing mechanism. Vertical clearance must be provided within the sampling arrangement to allow the turntable to be centred above the spindle. Also the turntable must be offered to the spindle in the correct rotational orientation for driving engagement with the spindle and to establish the correct angular location of the first sample location relative to the sampling mechanism so that the samples are taken in the predetermined order.